In order to arrange for a capacitance function or a capacitor on a substrate in the manufacture of integrated circuits, an insulating layer has been used between e.g. a layer of polycrystalline silicon and a layer of monocrystalline silicon, whereat a groove or the like insulates the capacitor formed from the surrounding region. In FIG. 1 is shown a cross section of a construction of a capacitor according to the above, in which an insulating layer 1 is situated between a polycrystalline silicon layer 2B and a monocrystalline silicon layer 3. A first metal conductor 4 is connected to a first metal plug 5, which is connected to a layer of polycrystalline silicon 2A on the monocrystalline silicon layer 3. A second metal conductor 6 is connected to a second metal plug 7, which is connected to the polycrystalline silicon layer 2B. Between the polycrystalline silicon layer 2B and the underlying monocrystalline silicon layer 3 the insulating layer 1 is situated, whereat the region delimited by the polycrystalline silicon layer 2B, the insulating layer 1 and the underlying part of the monocrystalline silicon layer 3 constitutes the capacitor, per se, which is connectable via the metal conductors 4 and 6.
Such a capacitor construction is easily manufactured using modern technique. In order to separate the capacitor construction from the other parts on the substrate, the substrate has been provided with grooves/trenches 8 having insulating wall material 9 filled with suitable filling. The polycrystalline layer in the capacitor, however, contributes to the resistive losses in the capacitor. The resistive losses make the capacitor less effective in decoupling of disturbances, generates more thermal noise, which may be a limiting factor in a radio construction. A filter construction in which a capacitor of the above described type is a part may cause high losses in the filter, e.g. make the filter less efficient.
In e.g. U.S. Pat. No. 5,013,680, U.S. Pat. No. 5,466,628 and WO-A 90 11 619 arrangements of capacitor functions/capacitors on substrates are shown.